Collapsibility, composition, and microstructure of loess in China

2016 ◽  
Vol 53 (4) ◽  
pp. 673-686 ◽  
Author(s):  
Zhen Liu ◽  
Fengyin Liu ◽  
Fuli Ma ◽  
Mei Wang ◽  
Xiaohong Bai ◽  
...  
Keyword(s):  
Structural Characteristics ◽  
Particle Morphology ◽  
High Porosity ◽  
X Ray ◽  
Collapse Potential ◽  
Metastable Structure ◽  
Clay Coating ◽  
Microstructural Model ◽  
Collapse Behavior ◽  
Clay Aggregates

The collapse potential, mineralogy, microstructure, and particle morphology of a loess from the Loess Plateau, China, were characterized by double oedometer testing, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and image analysis to elucidate the origin of its collapse behavior. Results show that the loess is highly collapsible with a maximum collapse index of 6.7% at a vertical stress of ∼200 kPa. The deposit contains both nonclay (i.e., quartz, albite, muscovite, and calcite) and clay (i.e., two chlorites) minerals. Microstructural, chemical, and image analyses indicate that interparticle calcite and clay cementation and silt particle morphology render the intact soil a metastable structure. Wetting-induced collapse is attributed to both primary and secondary microstructure features. The former is the abundance of weakly cemented, unsaturated, porous pure clay and clay–silt mixture aggregates whose slaking upon wetting initiates the overall structural collapse, while the latter consists of high porosity, unstable particle contacts, and clay coating on silt particles that act synergistically to augment the collapse. A conceptual microstructural model of a four-tiered hierarchy (i.e., primary clay and silt particles, clay aggregates and clay-coated silt particles, clay–silt mixture aggregates, and cemented aggregate matrix) is proposed to represent its structural characteristics and to account for its high collapsibility.

Morphological, Structural and Optical Characteristics of Porous GaN Fabricated by UV-Assisted Electrochemical Etching

2020 ◽  
Vol 301 ◽  
pp. 3-11
Author(s):  
Nurul Syuhadah Mohd Razali ◽  
Alhan Farhanah Abd Rahim ◽  
Rosfariza Radzali ◽  
Ainorkhilah Mahmood ◽  
Muhammad Faiz Bahrol Anuar
Keyword(s):  
Pore Structure ◽  
Current Density ◽  
Uv Light ◽  
Electrochemical Etching ◽  
Structural Characteristics ◽  
Peak Shift ◽  
High Porosity ◽  
Etching Technique ◽  
X Ray ◽  
Force Microscopy

The fabrication of porous GaN (PGaN) by UV-assisted electrochemical etching with a variations of current densities (40, 60, and 80 mA/cm2) for 60 min in electrolytes consisting of 4% KOH are reported. Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to characterize the morphological and structural characteristics of the PGaN. All PGaN sample prepared by electrochemical etching technique produced a hexagonal-like pore shape. FESEM images demonstrated that the pore uniformity and porosity are affected significantly by the current density. The PGaN sample fabricated with 80 mA/cm2 produces a uniform and high porosity structure compared to other PGaN sample. This shows that the morphology and structural characteristic of PGaN are increase with the increase of current density. The EDX result revealed significant Ga and N atom presence in all samples. However, the O atom only presence in sample etched with 80 mA/cm2 implying that the etching process is occur vigorously in this sample. The AFM verified that the surface roughness and the pore depth are increased as current density increased. There were relatively large variations of the peak intensities for 2Theta-scan patterns as exposed by XRD. The peak shift for PGaN sample relative to as-grown was inconsistent and the changed was relatively small. Raman intensity found to be enhanced with the increase in current density and among the PGaN sample, the E2(high) peak for sample prepared with 60mA/cm2 and 80mA/cm2 was observed to be slightly shifted to lower frequency. The PL spectra displayed that the porosity has high impact on the PL peak intensity. . Overall, this proved that with the usage of low power UV light, the pore structure still can be produced as good as pore structure fabricated with high power UV light.

scholarly journals Applicability of X-ray computed tomography for concrete cellular structure analysis

2021 ◽  
Vol 2124 (1) ◽  
pp. 012007
Author(s):  
M S Lebedev ◽  
M I Kozhukhova ◽  
E V Voitovich
Keyword(s):  
Computed Tomography ◽  
Cellular Structure ◽  
Structural Integrity ◽  
Structural Characteristics ◽  
Cement Matrix ◽  
High Porosity ◽  
X Ray ◽  
X Ray Computed ◽  
Average Size ◽  
Cellular Concrete

Abstract Nowadays, the researchers of materials sciences area, use direct and indirect methods such as microscopy, porosimetry, etc. for studying structural characteristics of materials. X-ray computed tomography is among one of the modern and widely used research analytical methods that provides 3D images of solid materials without any preliminary preparation, such as crashing of sample, and violation of its structural integrity. To demonstrate the potential possibilities of X-ray computed tomography, in this research matrices with cellular structure using portland cement-based cellular concrete was studied as an example. The study showed that the pore structure of cellular concrete is dominated by capillary pores with a diameter of up to 200 um. The majority of pores did not exceed 1.6 mm in diameter, that formed during the foaming process. The calculated average size of the volumetric distribution of air voids was 0.95 mm. About 80% of large pores of a cellular concrete specimen with an average size of about 1 mm determines high porosity of the composite which is consistent with its average density values. The study of interpore structure partition using X-ray computed tomography allows for evaluation the difference in thickness from 10 um to 0.6 mm in the zones of “confluence” of large pores. The porosity of cement matrix, including individual pores with sizes from -30 to 250 um, was about 16.5%. The cement matrix is dominated by the products of cement hydration with capillary and “gel” pores. There are few nonreacted cement particles that are evenly distributed throughout the volume of the composite. To obtain more complete information about the structure of cellular concrete or any other composite, it is necessary to perform complex studies applying not only X-ray computer tomography technique, also scanning electron microscopy for evaluation of chemical analysis to identify mineral phases present and correlate them with absorption intensity of X-ray radiation on tomographic images.

A High Resolution Study of G.P. Zones in Aluminum - 4.2 at % Silver

1982 ◽  
Vol 40 ◽  
pp. 722-723 ◽  
Author(s):  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Computer Simulations ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Resolution Study

The phenomenon of clustering in Al-Ag alloys has been extensively studied since the early work of Guinierl, wherein the pre-precipitation state was characterized as an assembly of spherical, ordered, silver-rich G.P. zones. Subsequent x-ray and TEM investigations yielded results in general agreement with this model. However, serious discrepancies were later revealed by the detailed x-ray diffraction - based computer simulations of Gragg and Cohen, i.e., the silver-rich clusters were instead octahedral in shape and fully disordered, atleast below 170°C. The object of the present investigation is to examine directly the structural characteristics of G.P. zones in Al-Ag by high resolution transmission electron microscopy.

Effect of synthesis and activation methods on the character of CoMo/ultrastable Y-zeolite catalysts

2021 ◽  
Vol 19 (1) ◽  
pp. 745-754
Author(s):  
Khoirina Dwi Nugrahaningtyas ◽  
Eddy Heraldy ◽  
Rachmadani ◽  
Yuniawan Hidayat ◽  
Indriana Kartini
Keyword(s):  
Electron Microscopy ◽  
Reduction Process ◽  
Particle Morphology ◽  
Zeolite Catalysts ◽  
X Ray Diffraction ◽  
Y Zeolite ◽  
X Ray ◽  
Irregular Particle ◽  
Transmission Electron ◽  
Pure Metals

Abstract The properties of three types of CoMo/USY catalysts with different synthesized methods have been studied. The sequential and co-impregnation methods followed by activation using calcination and reduction process have been conducted. The properties of the catalysts were examined using Fourier-transform-infrared (FTIR) spectroscopy, X-ray diffraction (XRD) with refinement, and surface area analyzer (SAA). The FTIR spectrum study revealed the enhanced intensity of its Bronsted acid site, and the XRD diffractogram pattern verified the composition of pure metals, oxides, and alloys in the catalyst. The SAA demonstrated the mesoporous features of the catalyst. Scanning electron microscopy showed an irregular particle morphology. Additional analysis using the transmission electron microscopy indicated that the metal has successfully impregnated without damaging the USY structure.

scholarly journals Sol-Gel Synthesis of the Double Perovskite Sr2FeMoO6 by Microwave Technique

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3876
Author(s):  
Jesús Valdés ◽  
Daniel Reséndiz ◽  
Ángeles Cuán ◽  
Rufino Nava ◽  
Bertha Aguilar ◽  
...  
Keyword(s):  
Particle Size ◽  
Hydrothermal Synthesis ◽  
Microwave Radiation ◽  
Structural Characteristics ◽  
Sol Gel ◽  
Synthesis Method ◽  
Double Perovskite ◽  
Synthesis Methods ◽  
X Ray ◽  
Sol Gel Synthesis

The effect of microwave radiation on the hydrothermal synthesis of the double perovskite Sr2FeMoO6 has been studied based on a comparison of the particle size and structural characteristics of products from both methods. A temperature, pressure, and pH condition screening was performed, and the most representative results of these are herein presented and discussed. Radiation of microwaves in the hydrothermal synthesis method led to a decrease in crystallite size, which is an effect from the reaction temperature. The particle size ranged from 378 to 318 nm when pH was 4.5 and pressure was kept under 40 bars. According to X-ray diffraction (XRD) results coupled with the size-strain plot method, the product obtained by both synthesis methods (with and without microwave radiation) have similar crystal purity. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques showed that the morphology and the distribution of metal ions are uniform. The Curie temperature obtained by thermogravimetric analysis indicates that, in the presence of microwaves, the value was higher with respect to traditional synthesis from 335 K to 342.5 K. Consequently, microwave radiation enhances the diffusion and nucleation process of ionic precursors during the synthesis, which promotes a uniform heating in the reaction mixture leading to a reduction in the particle size, but keeping good crystallinity of the double perovskite. Precursor phases and the final purity of the Sr2FeMoO6 powder can be controlled via hydrothermal microwave heating on the first stages of the Sol-Gel method.

scholarly journals Vacuum-Free and Highly Dense Nanoparticle Based Low-Band-Gap CuInSe2 Thin-Films Manufactured by Face-to-Face Annealing with Application of Uniaxial Mechanical Pressure

Coatings ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 484
Author(s):  
Matthias Schuster ◽  
Dominik Stapf ◽  
Tobias Osterrieder ◽  
Vincent Barthel ◽  
Peter J. Wellmann
Keyword(s):  
Thin Films ◽  
Band Gap ◽  
Coarse Grained ◽  
High Porosity ◽  
Low Band Gap ◽  
Seeding Layer ◽  
X Ray ◽  
Face To Face ◽  
Copper Indium ◽  
Vis Spectroscopy

Copper indium gallium sulfo-selenide (CIGS) based solar cells show the highest conversion efficiencies among all thin-film photovoltaic competition. However, the absorber material manufacturing is in most cases dependent on vacuum-technology like sputtering and evaporation, and the use of toxic and environmentally harmful substances like H2Se. In this work, the goal to fabricate dense, coarse grained CuInSe2 (CISe) thin-films with vacuum-free processing based on nanoparticle (NP) precursors was achieved. Bimetallic copper-indium, elemental selenium and binary selenide (Cu2−xSe and In2Se3) NPs were synthesized by wet-chemical methods and dispersed in nontoxic solvents. Layer-stacks from these inks were printed on molybdenum coated float-glass-substrates via doctor-blading. During the temperature treatment, a face-to-face technique and mechanically applied pressure were used to transform the precursor-stacks into dense CuInSe2 films. By combining liquid phase sintering and pressure sintering, and using a seeding layer later on, issues like high porosity, oxidation, or selenium- and indium-depletion were overcome. There was no need for external Se atmosphere or H2Se gas, as all of the Se was directly in the precursor and could not leave the face-to-face sandwich. All thin-films were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV/vis spectroscopy. Dense CISe layers with a thickness of about 2–3 µm and low band gap energies of 0.93–0.97 eV were formed in this work, which show potential to be used as a solar cell absorber.

scholarly journals Mechanochemical Preparation of Slow Release Fertilizer Based on Glauconite–Urea Complexes

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 507 ◽  
Author(s):  
Maxim Rudmin ◽  
Elshan Abdullayev ◽  
Alexey Ruban ◽  
Ales Buyakov ◽  
Bulat Soktoev
Keyword(s):  
Milling Time ◽  
Slow Release ◽  
Mechanochemical Activation ◽  
Structural Characteristics ◽  
Fluorescence Analysis ◽  
Planetary Mill ◽  
X Ray Diffraction ◽  
Mechanochemical Method ◽  
X Ray ◽  
Slow Release Fertilizers

We investigated the mechanochemical synthesis of complex slow release fertilizers (SRF) derived from glauconite. We studied the effectiveness of the mechanical intercalation of urea into glauconite using planetary and ring mills. The potassium-nitric complex SRFs were synthesized via a mechanochemical method mixing glauconite with urea in a 3:1 ratio. The obtained composites were analyzed using X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence analysis, and infrared spectroscopy. The results show that as duration of mechanochemical activation increases, the mineralogical, chemical, and structural characteristics of composites change. Essential modifications associated with a decrease in absorbed urea and the formation of microcrystallites were observed when the planetary milling time increased from 5 to 10 min and the ring milling from 15 to 30 min. Complete intercalation of urea into glauconite was achieved by 20 min grinding in a planetary mill or 60 min in a ring mill. Urea intercalation in glauconite occurs much faster when using a planetary mill compared to a ring mill.

Nanostructured TiO2-Based Composites for Light Absorption

2014 ◽  
Vol 975 ◽  
pp. 207-212
Author(s):  
Dayse I. dos Santos ◽  
Olayr Modesto Jr. ◽  
Luis Vicente A. Scalvi ◽  
Americo S. Tabata
Keyword(s):  
Metal Oxide ◽  
Light Absorption ◽  
Structural Characteristics ◽  
Sol Gel ◽  
Second Phase ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Oxide Powders

Metal oxide nanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first process produces directly a two-phase material, while the sol-gel powder never showed second phase below 600°C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

The high-pressure cadmium borate Cd6B22O39·H2O

2015 ◽  
Vol 70 (3) ◽  
pp. 183-190 ◽  
Author(s):  
Gerhard Sohr ◽  
Nina Ciaghi ◽  
Klaus Wurst ◽  
Hubert Huppertz
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Pressure High Temperature ◽  
Cell Dimensions ◽  
Temperature Experiment ◽  
Unit Cell Dimensions ◽  
Ir And Raman

AbstractSingle crystals of the hydrous cadmium borate Cd6B22O39·H2O were obtained through a high-pressure/high-temperature experiment at 4.7 GPa and 1000 °C using a Walker-type multianvil apparatus. CdO and partially hydrolyzed B2O3 were used as starting materials. A single crystal X-ray diffraction study has revealed that the structure of Cd6B22O39·H2O is similar to that of the type M6B22O39·H2O (M=Fe, Co). Layers of corner-sharing BO4 groups are interconnected by BO3 groups to form channels containing the metal cations, which are six- and eight-fold coordinated by oxygen atoms. The compound crystallizes in the space group Pnma (no. 62) [R1=0.0379, wR2=0.0552 (all data)] with the unit cell dimensions a=1837.79(5), b=777.92(2), c=819.08(3) pm, and V=1171.00(6) Å3. The IR and Raman spectra reflect the structural characteristics of Cd6B22O39·H2O.

scholarly journals Surface Texture of Microcrystalline Tunnel-Structured Manganese(IV) Oxides: Nitrogen Sorptiometry and Electron Microscopy Studies

2002 ◽  
Vol 20 (7) ◽  
pp. 619-632 ◽  
Author(s):  
A.A. Ali ◽  
F.A. Al-Sagheer ◽  
M.I. Zaki
Keyword(s):  
Electron Microscopy ◽  
Chemical Composition ◽  
Surface Texture ◽  
Particle Morphology ◽  
High Resolution Electron Microscopy ◽  
Surface Chemical ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Surface Chemical Composition ◽  
Resolution Electron

Three different modifications of manganese(IV) oxide, viz. cryptomelane, nsutite and todorokite-like, were synthesized by hydrothermal methods. The bulk chemical composition, phase composition, crystalline structure and particle morphology of the resulting materials were determined by thermogravimetry, atomic absorption spectroscopy, X-ray diffractometry, infrared spectroscopy and scanning electron microscopy. The surface chemical composition, texture and structure were assessed using X-ray photoelectron microscopy, nitrogen sorptiometry and high-resolution electron microscopy. The results highlighted the hydrothermal conditions under which such tunnel-structured modifications of manganese(IV) oxide can be successfully synthesized. Moreover, they revealed that (i) the bulk was microcrystalline, (ii) the crystallites were either fibrils (cryptomelane and nsutite) or rod-like (todorokite) with low-index exposed facets, (iii) the surface chemical composition mostly reflected that of the bulk and (iv) the surface texture was linked with high specific areas, slit-shaped mesopores associated with particle interstices and micropores which allowed surface accessibility to the bulk tunnels of the test oxides. The application of such test oxides as shape-selective oxidation catalysts appears worthy of investigation.

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